The present invention relates to a method for manufacturing a screen for a cathode ray tube, and particularly to a method for manufacturing a screen for a cathode ray tube in which emitting luminance is enhanced through enhancing the smoothness and compactness of the screen.
Generally, a screen, called a phosphor layer, for a cathode ray tube is manufactured through coating a slurry containing red, green or blue emitting phosphors on the inner surface of a panel, carrying out drying, exposing and developing processes, and then coating the remaining two phosphors in a predetermined dot or stripe pattern and in the same manner as described above. A thin aluminium layer is formed at a predetermined distance from the surface of the thus-obtained screen.
The prior art pattern-forming process of the phosphor layer will be described in detail with reference to the attached FIGS. 1A-1C.
Phosphor slurry is prepared by dispersing phosphors in a mixture of polyvinyl alcohol having a polymerization degree of 1,500 to 2,000 and a saponification degree of 80 to 90 mol % and, playing the role of attaching the phosphor onto the panel surface, a photosensitive sodium dichromate, a surfactant which facilitates the mixing of water with organic materials, an acryl emulsion and distilled water. Generally, the specific gravity of the thus-obtained phosphor slurry ranges from 1.280 to 1.299, with its viscosity ranging from 31 to 45 cps.
A phosphor slurry prepared by dispersing the first phosphor, for example, a green phosphor slurry prepared by dispersing green emitting phosphors is coated on the inner surface of the panel (1), on the upper surface of the black matrix (2) and dried to give a photosensitive layer. The prescribed parts of the layer are exposed to ultraviolet light using a shadow mask. At this time, the difference of solubility in water between the exposed parts and un-exposed parts of the photosensitive layer, comes into play. Through the developing process afterward, water soluble parts are dissolved out and water resist parts remain on the surface of the panel (1) to form the first phosphor layer, for example, a green emitting phosphor layer (FIG. 1A). Following the same method as described above, the second and third phosphor layers, for example, blue (FIG. 1B) and red (FIG. 1C) emitting phosphor layers, are formed to complete the phosphor pattern of each color.
According to the above-mentioned method, the first phosphor layer is stable, however, the dot (or stripe) in the second phosphor layer accumulates to the first phosphor as illustrated in FIG. 1B, and in the third layer, correspondingly accumulates and leans toward the pre-formed first and second phosphor as illustrated in FIG. 1C. This attraction is based on moisture absorption by pre-formed layer(s). For the second phosphor, during the drying process after coating the second phosphor slurry, absorption of the moisture from the second phosphor slurry by the pre-formed first phosphor layer results in the inclination of the second phosphor toward the first phosphor side. For the third phosphor, during the drying process after coating the third phosphor slurry, absorption of the moisture from the third phosphor slurry by the pre-formed first and second phosphor layers also results in the inclination of the third phosphor toward the first and second phosphor layers and this gives a dot (or stripe) of the third phosphor having a thick periphery and a relatively thin center. Consequently, the prior art process does not provide a smooth phosphor layer and may cause hole-perforation, especially in the third phosphor layer. The uneven phosphor layer deteriorates the smoothness of an aluminium layer manufactured through the subsequent filming layer manufacturing process, aluminium deposition process and baking process. The deterioration of the smoothness of the aluminium layer means the deterioration of the ratio of mirror reflection of the layer. This ultimately results in the deterioration of emission luminance of the phosphor layer.